favourite_languages={
    'jen':'python',
    'sarah':'c',
    'edward':'ruby',
    'phil':'python',
}
print("The following languages have been mentioned: ")
for language in favourite_languages.values():
    print(language.title())
#去除重复的元素
print("The following languages have been mentioned:")
for language in set(favourite_languages.values()):
    print(language.title())
#集合也有花括号，但没有键值对